Multiple piece piston

ABSTRACT

The subject matter of this specification can be embodied in, among other things, an assembly that includes a piston having a piston inner surface defining a cylindrical cavity and includes a first axial portion, a piston face at a first end of the first axial portion, a second axial portion at a second end of the first axial portion, and a helical piston thread defined upon the piston inner surface, a bushing configured to contact the piston inner surface, and a lock nut configured to engage the piston and the bushing.

TECHNICAL FIELD

This instant specification relates to an aircraft thrust reverseractuation system.

BACKGROUND

Contemporary aircraft engines may include a thrust reverser actuationsystem (TRAS) to assist in reducing the aircraft speed during landing.Typical thrust reversers include one or more movable transcowls that,when in the active position, reverse at least a portion of the airflowpassing through the engine.

Mechanically synchronized locking actuators used in TRAS use pistons tomaintain synchronization with other actuators through an acme lead screwand lead screw nut assembly. The TRAS actuators are expected to holdhigh loads in the locked position and achieve smooth synchronization formany cycles. This is typically done with a lead screw nut that has aradially interior threads to engage the lead screw. The lead screw nuttypically also has a groove on the radially external diameter to engagea lock key (or lock fingers such as used in finger lock actuators) tomechanically lock the actuator when it is not in use. Examples ofsynchronized actuators incorporating key type locks are found in U.S.Pat. Nos. 8,715,132 and 8,932,176.

Historically, piston assembly designs have been able to meetrequirements with a lock nut material that achieves both high strengthand low friction. In other historical piston assemblies, the lockingfeature is machined into the piston, but this method can be difficultfrom a manufacturing perspective and can lead to higher costs. Recently,aircraft loads have been increasing, and new designs will be needed tomeet these requirements.

SUMMARY

In general, this document describes an aircraft thrust reverseractuation system.

In a general aspect, an assembly includes a piston having a piston innersurface defining a cylindrical cavity and includes a first axialportion, a piston face at a first end of the first axial portion, asecond axial portion at a second end of the first axial portion, and ahelical piston thread defined upon the piston inner surface, a bushingconfigured to contact the piston inner surface, and a lock nutconfigured to engage the piston and the bushing.

Various implementations can include some, all, or none of the followingfeatures. The bushing can include a tubular cylindrical body having abushing outer surface configured to concentrically contact the pistoninner surface. The bushing can include a tubular cylindrical body havinga bushing inner surface, and a helical bushing thread defined upon thebushing inner surface. The lock nut can have a cylindrical outer surfaceand a helical nut thread defined upon the cylindrical outer surface. Thehelical nut thread can be configured to mate with a helical pistonthread defined upon the piston inner surface. The assembly can alsoinclude a cylindrical first collection of tines arranged upon an axialend of the bushing, and a cylindrical second collection of tinesarranged upon an axial end of the lock nut configured to rotationallyengage the cylindrical first collection of tines. The assembly can alsoinclude a lead screw arranged within the cylindrical cavity. The leadscrew can include a helical lead screw thread arranged to engage ahelical bushing thread defined upon a tubular inner surface of thebushing. The assembly can also include a locking pin configured torotationally engage the bushing to the piston.

In another general aspect, a method of assembling a piston assemblyincludes inserting a bushing into a cylindrical cavity defined by apiston inner surface of a piston, contacting the piston inner surfacewith a bushing outer surface of a tubular cylindrical body of thebushing, threading a lock nut onto a helical piston thread defined uponthe piston, and rotationally engaging a cylindrical first collection oftines arranged upon an axial end of the bushing, and a cylindricalsecond collection of tines arranged upon an axial end of the lock nut.

Various implementations can include some, all, or none of the followingfeatures. The method can also include axially constraining, by thethreading, the bushing between the lock nut and a piston face at a firstend of a first axial portion of the piston inner surface, wherein thehelical piston thread is defined upon a second axial portion of thepiston inner surface. The method can also include providing the pistonassembly. The piston inner surface can include a first axial portion, apiston face at a first end of the first axial portion, and a secondaxial portion at a second end of the first axial portion, where thehelical piston thread is defined upon the piston inner surface. Thebushing can include a tubular cylindrical body having a bushing outersurface configured to concentrically contact the piston inner surface.The bushing can include a tubular cylindrical body having a bushinginner surface, and a helical bushing thread defined upon the bushinginner surface. The lock nut can include a cylindrical outer surface anda helical nut thread defined upon the cylindrical outer surface, whereinthe helical nut thread is configured to mate with a helical pistonthread defined upon the piston inner surface. The method can alsoinclude threading a lead screw through the cylindrical cavity, whereinthe lead screw comprises a helical lead screw thread arranged to engagea helical bushing thread defined upon a tubular inner surface of thebushing. The method can also include rotating the lead screw relative tothe piston, the bushing, and the lock nut, converting rotation of thelead screw into linear motion of the piston, the bushing, and the locknut, and moving the piston, the bushing, and the lock nut linearlyrelative to the lead screw. The process can also include inserting alocking pin into a cavity defined between the piston and the bushing,rotationally engaging, by the locking pin, the piston to the bushing,and transferring, by the locking pin, a rotational force between thepiston and the bushing.

The systems and techniques described here may provide one or more of thefollowing advantages. First, a three-piece piston can provide improvedperformance relative to one-piece designs. The components of thethree-piece piston can made from different materials in order toincrease the performance of the piston. The piston can include a lockkey groove made out of a high strength material to react a load fromload keys. The locking nut can be made from a high hardness material toreduce friction. The piston can be coated or otherwise treated toincrease its wear properties.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of an example turbofan jet engine assemblywith a portion of the outer nacelle cut away for clarity.

FIG. 2 is a schematic view of the engine assembly of FIG. 1 with anexemplary thrust reverser.

FIG. 3 is a schematic view of the engine assembly of FIG. 1 with analternative exemplary thrust reverser.

FIG. 4 is a perspective view of an example hydraulic actuator.

FIG. 5 is a cross sectional view of an example three-piece pistonassembly of the hydraulic actuator of FIG. 4.

FIG. 6 is a cross sectional view of another example three-piece pistonassembly of the hydraulic actuator of FIG. 4.

FIG. 7 is a flow diagram of an example process for assembling theexample three-piece piston assembly of FIG. 5.

DETAILED DESCRIPTION

This document describes systems and techniques for reversing aircraftturbine engine airflow, including a three-piece piston assembly. Athrust reverser with at least one movable cowl element (i.e., at leastone transcowl), which is movable to and from a reversing position, maybe used to change the direction of the bypass airflow. In the reversingposition, the movable cowl element may be configured to reverse at leasta portion of the bypass airflow. As the moveable cowl element is movedinto and out of the reversing position by a hydraulic actuator, theforces (e.g., thrust, air resistance) interacting with the moveable cowlelement can cause sudden changes in load presented to the actuator. Suchforces can be damaging to the system; for example, a hydraulic actuatormay initially push the moveable cowl element from the stowed positiontoward the deployed position, and at some point mid-stroke theaerodynamic forces on the element may provide powerful additional forcesthat urge the moveable cowl element toward deployment. Such forces maycause the moveable cowl element and/or the actuator to hit their end oftravel with an impact that is sufficient to cause damage to the system.

In general, the systems described below overcome this problem by using ahydraulic valve that controls fluid flow through the hydraulic actuator.The valve is mechanically linked to the actuator in a manner such thatthe valve can vary the fluid flow through the actuator depending on theposition of the actuator. The valve can be constructed such that when inuse, the fluid flow through the actuator can be restricted atpredetermined positions, such as near an end of travel to resistassistive aerodynamic loads, for example, to slow actuator deployment orto soften impacts against the end of travel.

Conventional cascade type thrust reverser actuation systems havehydraulic actuators that include an arm that is attached to the moveablecowl element, and a feedback screw that moves in proportion to the arm.Such thrust reversers also have mounting points to which positionsensors (e.g., LVDTs) can be attached. These position sensors areconfigured to sense the position of the feedback screw, and therebyprovide a feedback signal that is representative of the position of themoveable cowl element. The valves described herein can be configured toattach to hydraulic actuators in place of such position sensors, and beactuated by the feedback screw.

FIG. 1 illustrates an example turbofan jet engine assembly 10 having aturbine engine 12, a fan assembly 13, and a nacelle 14. Portions of thenacelle 14 have been cut away for clarity. The nacelle 14 surrounds theturbine engine 12 and defines an annular airflow path or annular bypassduct 16 through the jet engine assembly 10 to define a generallyforward-to-aft bypass airflow path, as schematically illustrated by thearrow 18. A combustion airflow is schematically illustrated by thearrows 19.

A thrust reverser with at least one movable element, which is movable toand from a reversing position, may be used to change the direction ofthe bypass airflow. In the reversing position, the movable element maybe configured to reverse at least a portion of the bypass airflow. Thereare several methods of obtaining reverse thrust on turbofan jet engineassemblies. FIG. 2 schematically illustrates one example of a thrustreverser 20 that may be used in the turbofan jet engine assembly 10. Thethrust reverser 20 includes a movable element 22. The movable element 22has been illustrated as a cowl portion that is capable of axial motionwith respect to the forward portion of the nacelle 14. A hydraulicactuator 24 may be coupled to the movable element 22 to move the movableelement 22 into and out of the reversing position. In the reversingposition, as illustrated, the movable element 22 limits the annularbypass area between the movable element 22 and the turbine engine 12, italso opens up a portion 26 between the movable element 22 and theforward portion of the nacelle 14 such that the air flow path may bereversed as illustrated by the arrows 28. An optional deflector or flap29 may be included to aid in directing the airflow path between themovable element 22 and the forward portion of the nacelle 14.

FIG. 3 schematically illustrates an alternative example of a thrustreverser 30. The thrust reverser 30 includes a movable element 32. Themovable element 32 has been illustrated as a deflector, which may bebuilt into a portion of the nacelle 14. A hydraulic actuator 34 may becoupled to the movable element 32 to move the movable element 32 intoand out of the reversing position. In the reversing position, shown inphantom and indicated at 36, the movable element 32 turns the airoutward and forward to reverse its direction as illustrated by thearrows 38. An optional deflector or flap 39 may be included to aid indirecting the airflow path outward.

In both illustrative examples, the thrust reverser changes the directionof the thrust force. Both the thrust reverser 20 and the thrust reverser30 have been described as hydraulically operated systems and a hydraulicactuator has been schematically illustrated. In some embodiments, thethrust reverser 20 and/or the thrust reverser 30 can be powered by otherfluids (e.g., pneumatic), by electro-mechanical actuators, or by anyother appropriate power source or actuator type.

FIG. 4 is a perspective view of an example hydraulic actuator 400. Insome embodiments, the hydraulic actuator 400 can be the examplehydraulic actuator 24 of FIG. 2 or the example hydraulic actuator 34 ofFIG. 3. The hydraulic actuator 400 includes a housing 402 and a gimbal404. In some embodiments, the gimbal 404 can be configured to removablyaffix the housing 402 to a structural member, such as the examplenacelle 14.

A rod end 410 is configured to extend and retract relative to thehousing 402. In some embodiments, the rod end 410 can be configured toremovably affix the hydraulic actuator 400 to a moveable element, suchas the example moveable element 22 or the example moveable element 32.The rod end 410 is configured to extend and retract linearly, relativeto the housing 402.

The hydraulic actuator 400 includes an actuator deploy port 420 and anactuator stow port 422. The hydraulic actuator 400 is configured toextend the rod end 410 when fluid (e.g., hydraulic fluid) is flowed tothe actuator deploy port 420 and retract the rod end 410 when fluid isflowed to the actuator stow port 422.

The housing 402 includes a mount point 440. The mount point 440 isconfigured for the removable attachment of a position sensor such as anLVDT. However, in the illustrated example, a control valve 450 isremovably affixed to the hydraulic actuator 400 at the mount point 440.The control valve 450 is a hydraulic valve that includes an inlet fluidport 452 and an outlet fluid port 454.

As aircraft loads increase, new piston designs are needed in order toprovide enough strength to maintain TRAS synchronization with otheractuators through an acme lead screw and lead screw nut assembly, whilealso being lightweight and economical to manufacture. FIG. 5 is a crosssectional view of an example three-piece piston assembly 500 of thehydraulic actuator of FIG. 4. In general, the design and implementationof the example piston assembly 500 provides such strength, weight, andmanufacturability.

In general, in order to meet larger loads, previous designs haveimplemented increases in lock nut sizes. However, increasing the locknut size can significantly increase the overall size and weight of anactuator used in weight-sensitive applications such as aircraft. Ingeneral, the piston assembly 500 solves this issue by splitting thepiston into three pieces that can be assembled together, and the threepieces can be designed to use different materials that can be selectedfor their respective features, all within the small space of the pistonhead and while still using conventional technology in regards tomanufacturing and assembly.

The piston assembly 500 includes an actuator piston 510, a bushing 520,a lock nut 530, and an actuator lead screw 540. The actuator piston 510has two radially interior surfaces that define an interior cavity 502.An axial portion 516 of the interior cavity 502 is defined by a surface512 that is smooth in order to engage a smooth surface 522 the bushing520. The axial portion 516 includes a piston face 513 at an end 518. Atan end 519, an axial portion 517 of the interior cavity 502 is definedby a surface 514 that is threaded to engage a threaded surface 534 ofthe lock nut 530.

The bushing 520 includes a surface 524. The surface 524 is defined as aradially interior thread configured to engage a threaded surface 542 ofthe actuator lead screw 540. A surface 522 is smooth and abuts thesurface 512 of the interior cavity 502 of the piston assembly 500.

A surface 544 of the actuator lead screw 540 is configured as a radiallyexterior surface that is smooth and designed to fit into the internalcavity 502 of the actuator piston 510.

An axial surface of the bushing 520 includes a collection of tines 526arranged as a castle feature and/or serrations. The lock nut 530includes a collection of tines 536 configured to engagingly mate withthe collection of tines 526. The tines 526 and the tines 536 areconfigured to engage axially in order to rotationally engage the locknut 530 with the bushing 520.

The lock nut 530 retains the bushing 520 within the internal cavity 502of the actuator piston 510. The lock nut 530 prevents rotation of thebushing 520 relative to the lock nut 530 when the lock nut 530 isinstalled into the actuator piston 510. The lock nut 530 is located atan end 550 of the actuator piston 510 proximal to the piston head. Thethreaded surface 534 is configured to engage to a corresponding threadof the threaded surface 514 on the radially interior diameter of theactuator piston 510. In its assembled configuration, the threadedsurface 534 matingly engages the threaded surface 514 in order toaxially retain the actuator piston 510 and the lock nut 530.

In some embodiments, each of the actuator piston 510, the bushing 520,the lock nut 530, and the actuator lead screw 540 can be formed fromdifferent materials. The materials can be selected based on the purposeand/or performance characteristics of each of these components. Forexample, the material used to manufacture the actuator piston 510 can beselected for high strength, such as 15-5 PH. The 15-5 PH alloy ismartensitic in structure in the annealed condition and is furtherstrengthened by a relatively low temperature heat treatment whichprecipitates a copper containing phase in the alloy. 15-5 PH is alsoreferred to as XM-12 in some specifications. In another example, thematerial used to manufacture the bushing 520 can be selected forlow-friction characteristics, such as GRAPH MO. GRAPH MO tool steel isan oil-hardening, graphitic tool steel that resists metal-to-metalsliding wear and galling. The steel contains a uniform dispersion ofgraphite particles which impart machinability and non-seizingcharacteristics. The graphite particles make the steel self-lubricatingin dry environments, and help to retain oil in lubricated environments.GRAPH MO tool steel can be hardened to over 60 Rockwell C from arelatively low hardening temperature, which minimizes size change anddistortion during heat treatment. In another example, the material usedto manufacture the lock nut 530 can be selected for high strength, suchas 15-5 PH, TOUGHMET, or similar materials. TOUGHMET is a high-strength,spinodally-hardened, copper nickel tin alloy that exhibits corrosionresistance, stress corrosion cracking resistance, anti-frictionproperties, is non-magnetic, and exhibits lubricity and wear resistanceunder severe loading conditions. Splitting the piston assembly 500 intomultiple pieces of different materials connected by one threaded and oneslotted interface can provide improved functionality, such as loadcapability.

FIG. 6 is a cross sectional view of another example three-piece pistonassembly 600 of the hydraulic actuator of FIG. 4. In general, the designand implementation of the example piston assembly 600 is a modificationof the example piston assembly 500 of FIG. 5.

In general, the piston assembly 600 differs from the piston assembly 500by the inclusion of a locking pin 610. The locking pin 610 is configuredto directly engage a lead screw nut 520′ to a piston 510′.

The piston assembly 600 includes an actuator piston 510′, a bushing520′, a lock nut 530′, and the actuator lead screw 540. The actuatorpiston 510′ defines a portion of an interior cavity 612. The bushing520′ defines another portion of the interior cavity 612. When theactuator piston 510′ and the bushing 520′ are assembled, the interiorcavity 612 is defined with an axial shape that is configured to acceptinsertion of the locking pin 610. In use, rotational forces between theactuator piston 510′ and the bushing 520′ are transferred primarilythough the locking pin 610, and little or no rotational force istransmitted through a surface 514′ that is threaded to engage a threadedsurface 534′.

FIG. 7 is a flow diagram of an example assembly process. The process 700may be performed, for example, to assemble the example piston assembly500 of FIG. 5 or the example piston assembly 6 of FIG. 6. For clarity ofpresentation, the description that follows uses the piston assembly 500as an example for describing the process 700. However, other embodimentsof the piston assembly 500 may be used to perform the process 700.

In general, during installation the bushing 520 is inserted into theactuator piston 510. The lock nut 530 is then installed. The tines 526engage the corresponding feature on the lock nut 530. The bushing 520and lock nut 530 then rotate together during installation until thebushing 520 abuts the actuator piston 510. This configuration allows forconvenient assembly of a multi-piece and multi-material synchronizedactuator piston.

At 710, a bushing is inserted into a cylindrical cavity defined by apiston inner surface of a piston. For example, the bushing 620 isinserted into the internal cavity 502 defined in the actuator piston510, such that the surface 522 is brought into contact with the surface512.

In some implementations, the piston inner surface can include a firstaxial portion, a piston face at a first end of the first axial portion,and a second axial portion at a second end of the first axial portion,where the helical piston thread is defined upon the piston innersurface. For example, the actuator piston 510 has two radially interiorsurfaces that define an interior cavity 502. The axial portion 516 ofthe interior cavity 502 is defined by the surface 512 and includes thepiston face 513 at the end 518. At the end 519, the axial portion 517 ofthe interior cavity 502 is defined by the surface 514.

At 620, the piston inner surface is contacted with a bushing outersurface of a tubular cylindrical body of the bushing. In someimplementations, the bushing include a tubular cylindrical body having abushing outer surface configured to concentrically contact the pistoninner surface. In some implementations, the bushing can include atubular cylindrical body having a bushing inner surface, and a helicalbushing thread defined upon the bushing inner surface. For example, thebushing 520 includes a surface 524. The surface 524 is defined as aradially interior thread configured to engage a threaded surface 542 ofthe actuator lead screw 540. The surface 522 is smooth and abuts thesurface 512 of the interior cavity 502 of the piston assembly 500.

At 730, a lock nut is threaded onto a helical piston thread defined uponthe piston. In some implementations, the lock nut can have a cylindricalouter surface and a helical nut thread defined upon the cylindricalouter surface, where the helical nut thread is configured to mate with ahelical piston thread defined upon the piston inner surface. Forexample, the surface 514 of the actuator piston 510 is threaded toengage the threaded surface 534 of the lock nut 530.

In some implementations, the process 700 can also include axiallyconstraining, by the threading, the bushing between the lock nut and apiston face at a first end of a first axial portion of the piston innersurface, wherein the helical piston thread is defined upon a secondaxial portion of the piston inner surface. For example, the lock nut 530retains the bushing 520 within the internal cavity 502 of the actuatorpiston 510. The lock nut 530 prevents rotation of the bushing 520relative to the lock nut 530 when the lock nut 530 is installed into theactuator piston 510, and the threaded surface 534 matingly engages thethreaded surface 542 in order to axially retain the actuator piston 510and the lock nut 530.

At 740, a cylindrical first collection of tines, arranged upon an axialend of the bushing, is engaged with a cylindrical second collection oftines arranged upon an axial end of the lock nut. For example, the tines526 and the tines 536 are configured to engage axially in order torotationally engage the lock nut 530 with the bushing 520.

In some implementations, the process 700 can also include providing thepiston assembly. For example, the actuator piston 510, the bushing 520,and the lock nut 530 can be provided for assembly into the pistonassembly 500.

In some implementations, the process 700 can also include threading alead screw through the cylindrical cavity, where the lead screw has ahelical lead screw thread arranged to engage a helical bushing threaddefined upon a tubular inner surface of the bushing. For example, thesurface 524 is defined as a radially interior thread configured toengage the threaded surface 542 of the actuator lead screw 540.

In some implementations, the process 700 can also include rotating thelead screw relative to the piston, the bushing, and the lock nut,converting rotation of the lead screw into linear motion of the piston,the bushing, and the lock nut, and moving the piston, the bushing, andthe lock nut linearly relative to the lead screw. For example, theactuator lead screw 540 can be rotated relative to the assembledconfiguration of the actuator piston 510, the bushing 520, and the locknut 530. As the actuator lead screw 540 rotates, the threaded surface542 threads and/or unthreads into and/or out of the surface 524. As theactuator lead screw 540 threads and unthreads, the rotational movementof the actuator lead screw 540 is converted into linear movement of theassembled configuration of the actuator piston 510, the bushing 520, andthe lock nut 530 relative to the actuator lead screw 540.

Although a few implementations have been described in detail above,other modifications are possible. For example, the logic flows depictedin the figures do not require the particular order shown, or sequentialorder, to achieve desirable results. In addition, other steps may beprovided, or steps may be eliminated, from the described flows, andother components may be added to, or removed from, the describedsystems. Accordingly, other implementations are within the scope of thefollowing claims.

What is claimed is:
 1. An assembly comprising: a piston having a pistoninner surface defining a cylindrical cavity and comprising: a firstaxial portion; a piston face at a first end of the first axial portion;a second axial portion at a second end of the first axial portion; and ahelical piston thread defined upon the piston inner surface; a bushingconfigured to contact the piston inner surface; and a lock nutconfigured to engage the piston and the bushing.
 2. The assembly ofclaim 1, wherein the bushing comprises a tubular cylindrical body havinga bushing outer surface configured to concentrically contact the pistoninner surface.
 3. The assembly of claim 2, wherein the bushingcomprises: a tubular cylindrical body having a bushing inner surface;and a helical bushing thread defined upon the bushing inner surface. 4.The assembly of claim 1, wherein the lock nut comprises a cylindricalouter surface and a helical nut thread defined upon the cylindricalouter surface.
 5. The assembly of claim 4, wherein the helical nutthread is configured to mate with a helical piston thread defined uponthe piston inner surface.
 6. The assembly of claim 1, further comprisinga cylindrical first collection of tines arranged upon an axial end ofthe bushing, and a cylindrical second collection of tines arranged uponan axial end of the lock nut configured to rotationally engage thecylindrical first collection of tines.
 7. The assembly of claim 1,further comprising a lead screw arranged within the cylindrical cavity.8. The assembly of claim 7, wherein the lead screw comprises a helicallead screw thread arranged to engage a helical bushing thread definedupon a tubular inner surface of the bushing.
 9. The assembly of claim 1,further comprising a locking pin configured to rotationally engage thebushing to the piston.
 10. A method of assembling a piston assembly, themethod comprising: inserting a bushing into a cylindrical cavity definedby a piston inner surface of a piston; contacting the piston innersurface with a bushing outer surface of a tubular cylindrical body ofthe bushing; threading a lock nut onto a helical piston thread definedupon the piston; and rotationally engaging a cylindrical firstcollection of tines arranged upon an axial end of the bushing, and acylindrical second collection of tines arranged upon an axial end of thelock nut.
 11. The method of claim 10, further comprising axiallyconstraining, by the threading, the bushing between the lock nut and apiston face at a first end of a first axial portion of the piston innersurface, wherein the helical piston thread is defined upon a secondaxial portion of the piston inner surface.
 12. The method of claim 10,further comprising providing the piston assembly.
 13. The method ofclaim 10, wherein the piston inner surface comprises: a first axialportion; a piston face at a first end of the first axial portion; and asecond axial portion at a second end of the first axial portion, whereinthe helical piston thread is defined upon the piston inner surface. 14.The method of claim 10, wherein the bushing comprises a tubularcylindrical body having a bushing outer surface configured toconcentrically contact the piston inner surface.
 15. The method of claim10, wherein the bushing comprises: a tubular cylindrical body having abushing inner surface; and a helical bushing thread defined upon thebushing inner surface.
 16. The method of claim 10, wherein the lock nutcomprises a cylindrical outer surface and a helical nut thread definedupon the cylindrical outer surface, wherein the helical nut thread isconfigured to mate with a helical piston thread defined upon the pistoninner surface.
 17. The method of claim 10, further comprising threadinga lead screw through the cylindrical cavity, wherein the lead screwcomprises a helical lead screw thread arranged to engage a helicalbushing thread defined upon a tubular inner surface of the bushing. 18.The method of claim 17, further comprising: rotating the lead screwrelative to the piston, the bushing, and the lock nut; convertingrotation of the lead screw into linear motion of the piston, thebushing, and the lock nut; and moving the piston, the bushing, and thelock nut linearly relative to the lead screw.
 19. The method of claim10, further comprising: inserting a locking pin into a cavity definedbetween the piston and the bushing; rotationally engaging, by thelocking pin, the piston to the bushing; and transferring, by the lockingpin, a rotational force between the piston and the bushing.